1. Field of the Invention
The present invention relates to a color image processing apparatus, and more particularly, to a color image processing apparatus capable of performing an excellent image discrimination as well as a color reproduction of both character and tonal images.
2. Description of the Prior Art
There is known a color image processing apparatus wherein color images such as character image, photographic image are separated into red R, Green G, and blue B for optical reading, and are recorded on a recording paper by an electrophotographic color output equipment in accordance with recording colors such as yellow Y, magenta M, cyan C, and black K (for color reproduction or color modification) converted from those separated colors.
FIG. 8 is a view illustrating the state of color discrimination (discrimination of chromatic color or achromatic color) in a color image processing apparatus mentioned above. In a cube shown in FIG. 8, the density of R is represented in the front in the horizontal direction, the density of B, in the vertical direction, and the density of G, in the direction of depth. Therefore, the front left corner at the bottom where all the densities of R, G, and B become zero represents white, and the back right corner at the top where all the densities become greatest represents black. Consequently, the region formed by linking white and black corresponds to an achromatic region (gray), and all others correspond to chromatic ones.
Here, in setting up an achromatic region, there arise contradictory problems subsequently described.
1 In order to minimize color ghost appearing in black character image (unnecessary color being generated around the edge of a black character) due to color doubling of each R, G, and B of a CCD sensor or chromatic aberration of a lens, it is desirable to expand the achromatic region as much as possible.
2 It is desirable to narrow the achromatic region as much as possible in order to accurately reproduce low-chroma colors (such as brown, dark blue, and purple) in the case of color tonal image.